A manipulator in a robot system losing the electric power is likely to “drop down” when a power failure or loss occur. Therefore some known manipulators are equipped with brakes that brake the movement of the manipulator arm and hold it in a certain position in such instances. For industrial manipulators which often have six or even more arm elements and thereto belonging rotational axes, each provided with a brake, this adds cost, size, weight and mechanical complexity.
Still a system like that is not able to transport the manipulator arm to a safe parking position but at best brakes the arm in a position close to where it is at the time of the power failure or a position determined by how the arm elements are balanced.
A few other solutions to reduce the unwanted effects of a power failure are previously known from and disclosed in the patent literature.
In U.S. Pat. No. 4,441,854 A, e.g., are disclosed three different systems which are used to brake the movement of a manipulator arm joint. No provision for positioning a manipulator arm in a certain position is shown. The movement of the arm is simple dampened or braked when dropping down.
In DE 102006057843 A1 is disclosed a system that uses energy stored in a spring to move a manipulator from a working position to a rest position.
All solutions described in this latter mentioned document involves large mechanical installations which also only provides for the manipulator to move to one predestined position when the loss of electric power occur.